The pharmacokinetics of ?-acetamidocaproic acid (AACA) were evaluated after the intravenous and oral administration of an antiulcer agent, zinc acexamate (ZAC) at a dose of 20?mg kg?1 (ion pairing between zinc and AACA) in rats with indomethacin-induced acute gastric ulcer (IAGU) or indomethacin-induced small bowel inflammation (ISBI).
In IAGU rats, the area under the curves (AUCs) of AACA were significantly smaller after both the intravenous (551 versus 1270 μg min ml?1) and oral (397 versus 562 μg min ml?1) administration of ZAC than controls, possible due to the significantly faster CLR of AACA. In ISBI rats, however, the AUCs of AACA were comparable with controls after both the intravenous and oral administration of ZAC.
In IAGU rats, the significantly smaller AUCs of AACA were due to the significantly faster CLR (due to the decreased urinary pH by indomethacin treatment) than controls. AACA has a basic secondary amine group. On the other hand, the comparable AUCs of AACA in ISBI rats were due to the comparable CLRs between ISBI and control rats.
AACA was excreted in the urine via active renal tubular secretion in all rats studied.
The elimination half-life of midazolam administered intravenously (5 mg kg?1) or orally (15 mg kg?1) was significantly decreased by 70% and 73%, respectively, 24 h after a single oral administration of ursodeoxycholic acid (UDCA, 300 mg kg?1) in rats. In the liver there was a significant enhancement of the hydroxylation of midazolam in the microsomes and expression of cytochrome P450 (CYP) 3A1 messenger RNA (mRNA) and CYP3A2 mRNA.
The Cmax and area under the curve (AUC)0–∞ of midazolam were significantly (1.8–2.3 fold) increased by the single oral treatment with UDCA (100 and 300 mg kg?1). Thus, the oral bioavailability, estimated from the AUC0–∞, of midazolam administered intravenously and orally was significantly (1.8- and 2.3-fold, respectively) increased by the treatment with UDCA.
Repeated administration of UDCA (300 mg kg?1 day?1) for 7 days did not alter the pharmacokinetics of midazolam administered intravenously or orally, and the expression of mRNA for CYP3As in the rat liver.
The study has shown that a single administration of UDCA in rats induces significant hepatic CYP3A activity and increases significantly the oral bioavailability of midazolam. Such effects on the pharmacokinetics of midazolam were little observed on the repeated administration of UDCA.
Prasugrel and clopidogrel are antiplatelet prodrugs that are converted to their respective active metabolites through thiolactone intermediates. Prasugrel is rapidly hydrolysed by esterases to its thiolactone intermediate, while clopidogrel is oxidized by cytochrome P450 (CYP) isoforms to its thiolactone. The conversion of both thiolactones to the active metabolites is CYP mediated. This study compared the efficiency, in vivo, of the formation of prasugrel and clopidogrel thiolactones and their active metabolites.
The areas under the plasma concentration versus time curve (AUC) of the thiolactone intermediates in the portal vein plasma after an oral dose of prasugrel (1 mg kg?1) and clopidogrel (0.77 mg kg?1) were 15.8 ± 15.9 ng h ml?1 and 0.113 ± 0.226 ng h ml?1, respectively, in rats, and 454 ± 104 ng h ml?1 and 23.3 ± 4.3 ng h ml?1, respectively, in dogs, indicating efficient hydrolysis of prasugrel and little metabolism of clopidogrel to their thiolactones in the intestine.
The relative bioavailability of the active metabolites of prasugrel and clopidogrel calculated by the ratio of active metabolite AUC (prodrug oral administration/active metabolite intravenous administration) were 25% and 7%, respectively, in rats, and 25% and 10%, respectively, in dogs.
Single intraduodenal administration of prasugrel showed complete conversion of prasugrel, resulting in high concentrations of the thiolactone and active metabolite of prasugrel in rat portal vein plasma, which demonstrates that these products are generated in the intestine during the absorption process.
In conclusion, the extent of in vivo formation of the thiolactone and the active metabolite of prasugrel was greater than for clopidogrel’s thiolactone and active metabolite.
Schizandrin is recognized as the major absorbed effective constituent of Fructus schisandrae, which is extensively applied in Chinese medicinal formula. The present study aimed to profile the phase I metabolites of schizandrin and identify the cytochrome P450 (CYP) isoforms involved.
After schizandrin was incubated with human liver microsomes, three metabolites were isolated by high-performance liquid chromatography (HPLC) and their structures were identified to be 8(R)-hydroxyl-schizandrin, 2-demethyl-8(R)-hydroxyl-schizandrin, 3-demethyl-8(R)-hydroxyl-schizandrin, by liquid chromatography-mass spectrometry (LC-MS), 1H-nuclear magnetic resonance (NMR), and 13C-NMR, respectively. A combination of correlation analysis, chemical inhibition studies, assays with recombinant CYPs, and enzyme kinetics indicated that CYP3A4 was the main hepatic isoform that cleared schizandrin. Rat and minipig liver microsomes were included when evaluating species differences, and the results showed little difference among the species.
In conclusion, CYP3A4 plays a major role in the biotransformation of schizandrin in human liver microsomes. Minipig and rat could be surrogate models for man in schizandrin pharmacokinetic studies. Better knowledge of schizandrin’s metabolic pathway could provide the vital information for understanding the pharmacokinetic behaviours of schizandrin contained in Chinese medicinal formula.
Zinc acexamate (ZAC) is ionized to zinc and ?-acetamidocaproic acid (AACA). Thus, the pharmacokinetics and tissue distribution of zinc and AACA after intravenous (50?mg kg?1) and oral (100?mg kg?1) administration of ZAC were evaluated in rats. Also the pharmacokinetics of AACA after intravenous (10, 20, 30, and 50?mg kg?1) and oral (20, 50, and 100?mg kg?1) administration of ZAC and the first-pass extractions of AACA at a ZAC dose of 20?mg kg?1 were evaluated in rats.
After oral administration of ZAC (20?mg kg?1), approximately 0.408% of the oral dose was not absorbed, the F value was approximately 47.1%, and the hepatic and gastrointestinal (GI) first-pass extractions of AACA were approximately 8.50% and 46.4% of the oral dose, respectively. The incomplete F value of AACA was mainly due to the considerable GI first-pass extraction in rats.
Affinity of rat tissues to zinc and AACA was low—the tissue-to-plasma (T/P) ratios were less than unity. The equilibrium plasma-to-blood cells partition ratios of AACA were independent of initial blood ZAC concentrations of 1, 5, and 10?µg ml?1—the mean values were 0.481, 0.490, and 0.499, respectively. The bound fractions of zinc and AACA to rat plasma were 96.6% and 39.0%, respectively.
5-{2-[4-(3,4-Difluorophenoxy)-phenyl]-ethylsulfamoyl}-2-methyl-benzoic acid (1) is a novel, potent, and selective agonist of the peroxisome proliferator-activated receptor alpha (PPAR-α).
In preclinical species, compound 1 demonstrated generally favourable pharmacokinetic properties. Systemic plasma clearance (CLp) after intravenous administration was low in Sprague–Dawley rats (3.2?±?1.4?ml min?1 kg?1) and cynomolgus monkeys (6.1?±?1.6?ml min?1 kg?1) resulting in plasma half-lives of 7.1?±?0.7?h and 9.4?±?0.8?h, respectively. Moderate bioavailability in rats (64%) and monkeys (55%) was observed after oral dosing. In rats, oral pharmacokinetics were dose-dependent over the dose range examined (10 and 50?mg kg?1).
In vitro metabolism studies on 1 in cryopreserved rat, monkey, and human hepatocytes revealed that 1 was metabolized via oxidation and phase II glucuronidation pathways. In rats, a percentage of the dose (approximately 19%) was eliminated via biliary excretion in the unchanged form.
Studies using recombinant human CYP isozymes established that the rate-limiting step in the oxidative metabolism of 1 to the major primary alcohol metabolite M1 was catalysed by CYP3A4.
Compound 1 was greater than 99% bound to plasma proteins in rat, monkey, mouse, and human.
No competitive inhibition of the five major cytochrome P450 enzymes, namely CYP1A2, P4502C9, P4502C19, P4502D6 and P4503A4 (IC50’s?>?30 μM) was discerned with 1.
Because of insignificant turnover of 1 in human liver microsomes and hepatocytes, human clearance was predicted using rat single-species allometric scaling from in vivo data. The steady-state volume was also scaled from rat volume after normalization for protein-binding differences. As such, these estimates were used to predict an efficacious human dose required for 30% lowering of triglycerides.
In order to aid human dose projections, pharmacokinetic/pharmacodynamic relationships for triglyceride lowering by 1 were first established in mice, which allowed an insight into the efficacious concentrations required for maximal triglyceride lowering. Assuming that the pharmacology translated in a quantitative fashion from mouse to human, dose projections were made for humans using mouse pharmacodynamic parameters and the predicted human pharmacokinetic estimates.
First-in-human clinical studies on 1 following oral administration suggested that the human pharmacokinetics/dose predictions were in the range that yielded a favourable pharmacodynamic response.
Pharmacokinetics of liquiritigenin, a candidate for inflammatory liver disease, and its two glucuronide conjugates, M1 and M2, were evaluated in rats. The hepatic and gastrointestinal first-pass effects of liquiritigenin were also evaluated in rats.
After oral administration of liquiritigenin at a dose of 20?mg kg?1, 1.07% of the dose was not absorbed from the gastrointestinal tract up to 24?h, and the F-value was only 6.68%. In vitro metabolism of liquiritigenin in S9 fractions of rat tissues showed that the liver and intestine were major tissues responsible for glucuronidation of liquiritigenin. The hepatic and gastrointestinal first-pass effects of liquiritigenin were approximately 3.67% and 92.5% of the oral dose, respectively.
Although the hepatic first-pass effect of liquiritigenin after absorption into the portal vein was 57.1%, the value was only 3.67% of the oral dose due to extensive gastrointestinal first-pass effect in rats. Therefore, the low F-value of liquiritigenin in rats was primarily attributable to an extensive gastrointestinal first-pass effect although liquiritigenin was well absorbed. Compared with rats, the higher F-value of liquiritigenin could be expected in humans.
The metabolism and excretion of a GABAA partial agonist developed for the treatment of anxiety, CP-409,092; 4-oxo-4,5,6,7-tetrahydro-1H-indole-3-carboxylic acid (4-methylaminomethyl-phenyl)-amide, were studied in rats following intravenous and oral administration of a single doses of [14C]CP-409,092.
The pharmacokinetics of CP-409,092 following single intravenous and oral doses of 4 and 15?mg kg?1, respectively, were characterized by high clearance of 169?±?18?ml min?1 kg?1, a volume of distribution of 8.99?±?1.46 l kg?1, and an oral bioavailability of 2.9% ± 3%.
Following oral administration of 100?mg kg?1 [14C]CP-409,092, the total recovery was 89.1% ± 3.2% for male rats and 89.3% ± 0.58% for female rats. Approximately 87% of the radioactivity recovered in urine and faeces were excreted in the first 48?h. A substantial portion of the radioactivity was measured in the faeces as unchanged drug, suggesting poor absorption and/or biliary excretion. There were no significant gender-related quantitative/qualitative differences in the excretion of metabolites in urine or faeces.
The major metabolic pathways of CP-409,092 were hydroxylation(s) at the oxo-tetrahydro-indole moiety and oxidative deamination to form an aldehyde intermediate and subsequent oxidation to form the benzoic acid. The minor metabolic pathways included N-demethylation and subsequent N-acetylation and oxidation.
The present work demonstrates that oxidative deamination at the benzylic amine of CP-409,092 and subsequent oxidation to form the acid metabolite seem to play an important role in the metabolism of the drug, and they contribute to its oral clearance and low exposure.
The in vitro metabolism of [14C]methoxychlor (MXC) has been studied using precision-cut liver slices from the Sprague–Dawley male rat, CD-1 male mouse, WE strain male Japanese quail and juvenile rainbow trout (Oncorhynchus mykiss). The results demonstrated integrated phase I and II metabolism of MXC and species differences in the metabolic profiles were observed.
In rat liver slice preparations, MXC was rapidly metabolized to bis-OH-MXC by sequential O-demethylation followed by subsequent O-glucuronidation forming bis-OH-MXC glucuronide. No mono-OH-MXC glucuronide was detected. The doubly conjugated metabolite, bis-OH-MXC 4-O-sulphate 4′-O-glucuronide, was also detected as a rat-specific metabolite.
Formation of mono-OH-MXC and its glucuronide was the main metabolic pathway in the mouse and Japanese quail. In contrast to the rat, only minor amounts of bis-OH-MXC glucuronide were detected. A reductively dehalogenated metabolite, dechlorinated mono-OH-MXC glucuronide, was observed only in mouse preparations.
In rainbow trout, comparative amounts of both mono- and bis-OH-MXC glucuronide were formed as the major metabolites. Unconjugated forms of these metabolites were detected only as minor products.
The different metabolic profiles of MXC observed in the four animal species are possibly due to substrate specificity of contributing CYP450 monooxgenase enzyme(s) in different animal species.
4-n-Nonylphenol and bisphenol A are endocrine disrupting chemicals that are mainly detoxified through glucuronidation. A factor that may modulate their glucuronidation rates is co-exposure to pharmaceuticals.
This study aimed to identify and characterize the potential metabolic interactions between 14 drugs and these two endocrine disruptors.
Nonylphenol and bisphenol A were co-incubated in freshly isolated rat hepatocytes with, drugs at a high concentration. Statistically significant metabolic inhibition of bisphenol A and nonylphenol biotransformation was observed with nine drugs (>50% inhibition by naproxen, salicylic acid, carbamazepine and mefenamic acid). Inhibition assays of UGT activity in rat liver microsomes revealed: 1) competitive inhibition by naproxen (Kiapp = 848.3 μM) and carbamazepine (Kiapp = 1023.1 μM), 2) no inhibition by salicylic acid suggesting another mechanism of inhibition.
Detoxification of nonylphenol and bisphenol A was shown to be impaired by excessive concentrations of many drugs and health risk assessment should therefore address this issue.
This study compared the hepatic glucuronidation of Picroside II in different species and characterized the glucuronidation activities of human intestinal microsomes (HIMs) and recombinant human UDP-glucuronosyltransferases (UGTs) for Picroside II.
The rank order of hepatic microsomal glucuronidation activity of Picroside II was rat > mouse > human > dog. The intrinsic clearance of Picroside II hepatic glucuronidation in rat, mouse and dog was about 10.6-, 6.0- and 2.3-fold of that in human, respectively.
Among the 12 recombinant human UGTs, UGT1A7, UGT1A8, UGT1A9 and UGT1A10 catalyzed the glucuronidation. UGT1A10, which are expressed in extrahepatic tissues, showed the highest activity of Picroside II glucuronidation (Km?=?45.1 μM, Vmax?=?831.9 pmol/min/mg protein). UGT1A9 played a primary role in glucuronidation in human liver microsomes (HLM; Km?=?81.3 μM, Vmax?=?242.2 pmol/min/mg protein). In addition, both mycophenolic acid (substrate of UGT1A9) and emodin (substrate of UGT1A8 and UGT1A10) could inhibit the glucuronidation of Picroside II with the half maximal inhibitory concentration (IC50) values of 173.6 and 76.2 μM, respectively.
Enzyme kinetics was also performed in HIMs. The Km value of Picroside II glucuronidation was close to that in recombinant human UGT1A10 (Km?=?58.6 μM, Vmax?=?721.4 pmol/min/mg protein). The intrinsic clearance was 5.4-fold of HLMs. Intestinal UGT enzymes play an important role in Picroside II glucuronidation in human.
Tissue distribution, metabolism, and disposition of oral (0.2–20?mg/kg) and intravenous (0.2?mg/kg) doses of [2-14C]dibromoacetonitrile (DBAN) were investigated in male rats and mice.
[14C]DBAN reacts rapidly with rat blood in vitro and binds covalently. Prior depletion of glutathione (GSH) markedly diminished loss of DBAN. Chemical reaction with GSH readily yielded glutathionylacetonitrile.
About 90% of the radioactivity from orally administered doses of [14C]DBAN was absorbed. After intravenous administration, 10% and 20% of the radioactivity was recovered in mouse and rat tissues, respectively, at 72?h. After oral dosing, three to four times less radioactivity was recovered, but radioactivity in stomach was mostly covalently bound.
Excretion of radioactivity into urine exceeded that in feces; 9–15% was exhaled as labeled carbon dioxide and 1–3% as volatiles in 72?h.
The major urinary metabolites were identified by liquid chromatography-mass spectrometry, and included acetonitrile mercaptoacetate (mouse), acetonitrile mercapturate, and cysteinylacetonitrile.
The primary mode of DBAN metabolism is via reaction with GSH, and covalent binding may be due to reaction with tissue sulphydryls.
The objective of this study was to investigate the effects of continuous St. John’s wort administration on single-dose pharmacokinetics of bupropion, a substrate of cytochrome P450 (CYP) 2B6, in healthy Chinese volunteers.
Eighteen unrelated healthy male subjects participated in this study. The single-dose pharmacokinetics of bupropion and hydroxybupropion were determined before (control) and after a long-term period of St. John’s wort intake (325?mg, three times a day for 14 days). Plasma concentrations of bupropion and hydroxybupropion were determined before and at 0.5, 1, 2, 3, 4, 5, 6, 8, 10, 12, 24, 36, 48, 60 and 72?h after dosing.
St. John’s wort treatment decreased the area under the concentration versus time curve extrapolated to infinity of bupropion in healthy volunteers from 1.4 μg·h ml?1 (95% confidence interval [CI]?=?1.2–1.6 μg·h ml?1) after bupropion alone to 1.2 μg·h ml?1 (95% CI?=?1.1–1.3 μg·h ml?1) during St. John’s wort treatment. St. John’s wort treatment increased the oral clearance of bupropion from 108.3 l h?1 (95% CI?=?95.4–123.0 l h?1) to 130.0 l h?1 (95% CI?=?118.4–142.7 l h?1). No change in the time to peak concentration (tmax) and the blood elimination half-life (t1/2) of bupropion was observed between the control and St. John’s wort-treated phases. However, the half-life of hydroxybupropion between two phases had a significant difference by a Student’s t test after logarithmic transformation. St. John’s wort treatment decreased the half-life of hydroxybupropion from 26.7?h (95% CI?=?23.8–29.9?h) to 24.4?h (95% CI?=?21.9–27.3?h).
St. John’s wort decreased, to a statistically significant extent, the plasma concentrations of bupropion, probably mainly by increasing the clearance of bupropion.
After both the intravenous and oral administration of zinc acexamate [ZAC; ion-pairing between zinc and ?-acetamidocaproic acid (AACA)] and cimetidine together, the areas under the curve (AUCs) of AACA were significantly greater [by 28.2 and 98.9% after the intravenous and oral administration, respectively, for control rats and 13.5 and 16.9% for indomethacin-induced acute gastric ulcer (IAGU) rats, respectively] than those of ZAC alone due to the significantly slower renal clearance (CLR). The significantly greater AUCs of AACA after both the intravenous and oral administration of ZAC and cimetidine together in control and IAGU rats could have been due to the inhibition of active renal tubular secretion of AACA by cimetidine.
After the intravenous and oral administration of both drugs together, the AUCs of cimetidine in control and IAGU rats were not different compared with those with cimetidine alone.
The in vitro metabolism of (?)-terpinen-4-ol was examined in human liver microsomes and recombinant enzymes.
The biotransformation of (?)-terpinen-4-ol was investigated by gas chromatography–mass spectrometry. (?)-Terpinen-4-ol was found to be oxidized to (?)-(1S,2R,4R)-1,2-epoxy-p-menthan-4-ol, major metabolic product by human liver microsomal P450 enzymes. The formation of metabolites of (?)-terpinen-4-ol was determined by relative abundance of mass fragments and retention times on GC.
CYP2A6 in human liver microsomes was a major enzyme involved in the oxidation of (?)-terpinen-4-ol by human liver microsomes, based on the following lines of evidence. First, of 11 recombinant human P450 enzymes tested, CYP2A6 had the highest activity for oxidation of (?)-terpinen-4-ol. Second, oxidation of (?)-terpinen-4-ol was inhibited by (+)-menthofuran. Finally, there was a good correlation between CYP2A6 maker activity and (?)-terpinen-4-ol oxidation activities in liver microsomes of 10 human samples.
Kinetic analysis showed that the Vmax/Km values for (?)-(1S,2R,4R)-1,2-epoxy-p-menthan-4-ol catalysed by liver microsomes of human sample HH-18 was 2.49 μL/min/nmol.
Human recombinant CYP2A6 catalysed (?)-(1S,2R,4R)-1,2-epoxy-p-menthan-4-ol with Vmax values of 13.9 nmol/min/nmol P450 and apparent Km values of 91 μM.
This study investigated the pharmacokinetics of thiamphenicol glycinate (TG) and thiamphenicol (TAP) in beagles (n?=?6) after intravenous administration of 50?mg/kg TG hydrochloride. Plasma concentrations of TG and TAP were measured by a HPLC-UV method.
Two-compartment model was selected to describe the pharmacokinetic characteristics of TG and TAP in vivo. Main parameters were as follows: AUC0–∞ of TAP and TG were 16,328?±?1682 µg·min/mL and 3943?±?546 µg·min/mL, respectively. The total plasma clearance (CL) of TG and TAP were 12.7?±?2.0?mL/min/kg and 2.5?±?0.3?mL/min/kg, respectively. Mean residence time (MRT) of TG and TAP were 27.5?±?3.5 and 207.2?±?20.2?min, respectively. The transformative rate constant (k1M) from TG to TAP was 0.0477?±?0.0028?min?1. The elimination rate constant (kM10) from TAP was 0.0238?±?0.0044?min?1. Coefficients of variation (CV) between observed values and predicted ones were 5.9% and 18.2%, respectively. The volume of distribution of the central compartment for TG (VC) and TAP (VCM) were 0.264?±?0.022?L/kg and 0.127?±?0.023?L/kg, respectively.
Pharmacokinetic parameters suggested that TG was presumably cleaved quickly by tissue esterase to release TAP for effectiveness in beagles after administration.
The purpose of the study was to evaluate the pharmacokinetic characteristics of a single, intravenous dose of antofloxacin hydrochloride in healthy Chinese male volunteers.
Twelve subjects were randomly assigned to groups that received a single, intravenous dose of 200, 300, or 400?mg antofloxacin hydrochloride in a three-way crossover design study. The serum and urine concentrations of antofloxacin were then assayed with high-performance liquid chromatography (HPLC). Major pharmacokinetic parameters and urine excretion were obtained up to 96?h after administration.
All three dosages were well tolerated. No clinically adverse reactions or abnormal laboratory results were detected.
After single-dose intravenous administration, antofloxacin hydrochloride exhibited linear pharmacokinetic characteristics with increasing dosages. The Cmax for groups treated with 200, 300, or 400?mg dosages were 2.05?±?0.38, 3.01?±?0.60, and 3.80?±?0.78?mg l?1, respectively; the areas under the curve from zero to infinity (AUC0–∞) were 25.14?±?2.95, 37.63?±?5.42, and 53.87?±?9.48?mg l?1·h, respectively. The t1/2β was around 20?h; and the urinary excretion was measured as being from 58% to 60% within 96?h.
Based on these results, 300?mg of antofloxacin hydrochloride administered once daily is the dose suggested for further investigation in multiple-dose administration studies.
Carvacrol (2-methyl-5-(1-methylethyl)-phenol), one of the main components occurring in many essential oils of the family Labiatae, has been widely used in food, spice and pharmaceutical industries.
The carvacrol glucuronidation was characterized by human liver microsomes (HLMs), human intestinal microsomes (HIMs) and 12 recombinant UGT (rUGT) isoforms.
One metabolite was identified as a mono-glucuronide by liquid chromatography/mass spectrometry with HLMs, HIMs, rUGT1A3, rUGT1A6, rUGT1A7, rUGT1A9 and rUGT2B7.
The study with a chemical inhibition, rUGT, and kinetics study demonstrated that rUGT1A9 was the major isozyme responsible for glucuronidation in HLMs, and rUGT1A7 played a major role for glucuronidation in HIMs.
Levels of urinary dialkylphosphates (DAPs) are currently used as a biomarker of human exposure to organophosphorus insecticides (OPs). It is known that OPs degrade on food commodities to DAPs at levels that approach or exceed those of the parent OP. However, little has been reported on the extent of DAP absorption, distribution, metabolism and excretion.
The metabolic stability of O,O-dimethylphosphate (DMP) was assessed using pooled human and rat hepatic microsomes. Time-course samples were collected over 2?h and analyzed by LC-MS/MS. It was found that DMP was not metabolized by rat or pooled human hepatic microsomes.
Male Sprague–Dawley rats were administered DMP at 20?mg kg?1 via oral gavage and i.v. injection. Time-course plasma and urine samples were collected and analyzed by LC-MS/MS. DMP oral bioavailability was found to be 107?±?39% and the amount of orally administered dose recovered in the urine was 30?±?9.9% by 48?h.
The in vitro metabolic stability, high bioavailability and extent of DMP urinary excretion following oral exposure in a rat model suggests that measurement of DMP as a biomarker of OP exposure may lead to overestimation of human exposure.
Cultured cryopreserved human hepatocytes are extensively used as a model system for studying drug metabolism, although they remain poorly characterized in respect of the major conjugation reactions glucuronidation and sulfation.
Using paracetamol (acetaminophen), we assessed eleven samples of cryopreserved human hepatocytes for their suitability to investigate the simultaneous glucuronidation and sulfation of xenobiotics and evaluated inhibitors of conjugation.
Kinetic characterization showed broadly similar values for paracetamol conjugation by hepatocytes (as reported in the literature for in vitro systems), with Km values of approximately 6 mM and 0.3 mM for glucuronidation and sulfation, respectively. Substantial interindividual differences were observed.
The hepatocytes demonstrated a strong dose-dependent switch from a preponderance of sulfation at low concentrations of paracetamol to glucuronidation at higher doses, consistent with routes of clearance in vivo.
A number of drugs, some of which such as probenecid and sulfinpyrazone are known to interact with paracetamol in vivo, were demonstrated to inhibit the sulfation and/or glucuronidation of paracetamol in hepatocytes, demonstrating the potential application of this model system for studying drug–drug interactions involving conjugation.